THE ULTIMATE RIBBON MIC MOD
So you want to do some recording on your own? And you are on a budget, because you are here, not walking to the studio? Or maybe you are just a gear geek like we drummers tend to be, and want to experiment at your home studio? This article is about a series of steps to modify a pair of chinese ribbon mics in hunt for the high class studio microphone performance of multiple price tag.
Anyone with some rather basic tools available, a lot of patience, a steady hand and another fifty bucks can modify a fifty buck ribbon microphone to challenge a high class studio microphone worth hundreds. How close you get, depends on your choices and skills and may in some extent be a matter of taste.
So get yourself a pair of cheap lollipop ribbon microphones and start the workshop. With some luck, a pair could be grabbed for a hundred bucks. As a word of warning, statements here are merely practical observations and feels, without advanced high tech technical analyses. Your experiment may vary.
Reading around about ribbon microphones gives you an overall impression of the capabilitys of a ribbon mic. Their limitation is the higher end of the frequency curve. Ribbon mics typically give up way earlier than studio condensers. When they drop out disturbing high frequency side noise from a string section, an acoustic guitar recording or the overhelming sizzle of cymbals on a drum set, this is actually an advantage, but to a certain limit. You dont want the mic to sound too dark or muddy. Many recording engineers value them as overheads for drums also due to their great response to transients.
Ribbon microphones in general have experienced a renaissance due to a couple of things. One reason is the extreme, crispy detail achieved by modern digital techniques, which has made audio engineers to seek for more silky sound. The typical charasteristics of a ribbon mic offers just that smoothiness. They roll off at higher frequencies giving the recording a vintage overall sound. This fact puts the goal of microphone modding to a perspective. More and more extended high frequency response is giving away the natural smoothiness of a ribbon mic. But where is the limit? Do we get even close?
The other reason for the renessaince is the development of magnets. Back in the 50's and 60's the magnets needed to be massive to be strong enough. They also losed their magnetism with time. New neodymium magnets (since the late 1980's) are much more powerful related to their size, they keep their strength - and they are cheap.
First step - remove mesh layers
When a conductor moves across a magnetic field, an electric pulse is created in the conductor. In ribbon microphones, there is an extremely thin aluminum ribbon, placed within a strong magnet field. Even the thickest ribbons are fragile, and could easily be blown off without protective mesh layers inside the microphone head. Depending on your brand they may vary. Removing all of the inner mesh layers will slightly enhance the output. After this the ribbon is more exposed to moving air, so placing the mic in the kick drum resonant head hole is not a good idea. But for drum overheads it doesn't matter.
One could imagine, that the best results are achieved without the microphone head housing grill alltogether. I didn't try this. After all, have a look at the legendary Coles 4038. With an apparently well covered head, this microphone is often regarded as a standard setter of ribbon microphones. It has an extremely flat response curve, responding moderately high frequencies. In some ribbon microphone shootouts some people find it a bit darkish, though. But still, this is the very microphone that was used eg on many Beatles recordings as a single drum overhead. The price tag has four numbers.
Second step - thinner ribbon
The next cheap, yet a bit more worksome step is to install a thinner ribbon. Your microphone data sheet may specify your ribbon already as 2.5 microns, as was in my case. Yet, when measured with a micrometer, a 32-fold ribbon gave a reading of 190µ. That makes 6 microns one fold. After handling different thichness foils it became obvious to me that a 6 µ ribbon is like from another world.
Cascade installs 2.5 micron ribbons on the Fat Heads, as many other brands and this was my first target. Finding the material for a new ribbon took actually most of the work. Ebay is a good start. Cutting and corrugating a 2.5 micron ribbon is not that difficult. I cut my very first ribbon too short. The second was long enough, and installing was succesfull at first try. Installation is more difficult than cutting and corrugating, especially to have the ribbon straight and at equal distances from the magnets. The ribbon is moderately fragile, and can't be pushed sideways. It's prone to break at the clamps if tension needs to be adjusted several times. Yet, if you are used to do some precision jobs, you should be okay.
Signal from the microphone has a significant sensitivity boost. My recording test showed a gain increase of 4-5dB. This drops, respectively, the effective internal noise from the microphone at equal recording levels because recording can be made with less gain on the preamp.
Third step - quality transformer
The 2.5 micron ribbon is good enough for high quality recording, but the result is limited to the quality of the transformer. As you may be aware of, these two parts are just about all there is to a ribbon microhone that makes the mic sound like it does. Disregarding the main design, like housing, magnet size and shape and ribbon measures (length, width), that is, which you can't change. So you must upgrade the transformer to reach higher ground.
On the market there are at least two great alternatives (Cinemag, Lundahl), and they only double your mic price, but multiply the output quality. Which one to choose, is more a matter of taste. There might be others too, there's tons of discussions about this on the net. I just trusted the major choice I ran into, and selected the Swedish Lundahl LL-2912. Installing the transformer requires some basic soldering skills. Also, depending on the microphone body, you might need to drill the hole from the body to the motor housing slightly larger. A 4mm hole is needed for the thicker leads of the Lundahl.
Fourth step - even thinner ribbon
There are also many ribbon microphones with even thinner, only 1.8 micron ribbon. If a step from 6 to 2.5 microns boosts the gain, will that also happen from 2.5 to 1.8µ and will the high frequency roll off level still be streched a bit higher? How much more difficult will the installation of a 1.8µ ribbon be?
As for the cutting and corrugating, I could not notice any significant change. Although the first ribbon broke in two while corrugating, I just was holding too tight on the ribbon while winding the corrugator. Installing again was sligthly more difficult. The ribbon tends to bend sideways, and it is not easy to put the first end in correct direction. Once the ribbon end is down, it is difficult to fix the orientation. Glueing the lower circuit board chip in place helps when putting down the first end of the ribbon. I later also used a small spot of sewing machine oil on the chip to engage the first end. This allows to adjust the orientation. I found a slightly moisted cotton swab as best way to lift and put the ribbon end in place.
The ribbon also has a tendency to stick onto various objects, as if there is some static electrical attraction. This makes the installation difficult. Also the reason could be the minor impurities of the material, which is only 99% pure aluminum.
As expected, again there was 1-2dB increase in gain, as well as slightly extended high frequency response.
Fifth step - the tuning mechanism
Despite the minor difficulties, the installation was far from impossible. Most difficult is the tuning. After attaching both ends, the ribbon is prone to break when trying to loosen or tighten the ribbon. I had experimented having the microphone body vertical after clamping the first end. When attaching a suitable weight (very light...) on the loose end, you might achieve the right tension rather easily. Yet, to find the correct weight takes a lot of efforts. And if you get ambitious and try to install other thickness ribbons, the weight should be forked again.
So, after some consideration, a solution was at hand. Build a tuning mechanism! With a few tiny moderations, it is possible to make a simple mechanism to control the ribbon tension easily and accurately with a screwdriver without detaching the ribbon end.

Building the tuner mechanism
On the Chinese lollipop type microphone motor, there is no room for moving parts at the top. But swapping the motor body upside down gives about 2 millimeters of clearance both ways. That's enough.
The mechanism consists of only three parts, a sandwitch structured sliding tray and a locking bar. The sliding tray is made of two small brass plates. They need to be locked to each other when put one on the other. Two small pins on the lower, thinner plate (1.5mm) and corresponding holes on the upper plate (2.5mm) take care of that. All fittings need to be as precise as possible, to avoid any twisting and winding during tuning, yet loose enough to allow moving back and forth in the ribbon's direction. Brass is a good choice for material to make the tray, as it is easy sliding, easy to machine and also insensitive to magnets.
A locking bar with a threaded hole for the adjusting screw is installed on top of the assembly. Detaching the magnets before drilling and threading the fixing screw holes helps when cleaning out the debris. The magnets on the tested microphones where initially really loosely glued and came off easily. I used Gorilla glue to reassemble the magnets. When the assembly is only lightly tightened, it is tunable on the fly. When done, tighten firmly and recheck the tuning. That's it.
Thinner - and even thinner!
The 1.8µ ribbon is a bit more difficult than 2.5, but only just. Then why not try even thinner ribbon? A step from 2.5 to 1.8 cuts around 30% of the ribbon mass, giving more sensitive response. An equal drop of ribbon mass from 1.8µ would be 1.2µ, a suitable next experiment. This time I accidentally tore the foil in two. Ouch, that is really, really thin. But again, when working carefully, the cutting and corrugating is rather easy. The cutting blade needs to be really sharp to avoid an uneven edge, which tends to make the ribbon cling to the shielding paper.
As before, the most difficult task is to center the ribbon and have it sitting straight. After this, it is just a matter of assembling the tuning mechanism locking bar and start tuning. After a few installations, the ribbon tension is rather easy to have initially close to right. Then, to tune the ribbon and ananalyse the frequency response, the microphone is connected to a DAW system. When gently tapping the microphone body, the ribbon resonates at it's charateristic resonance. Check where the last and most powerful frequencies are located. While having the locking bar screws only slightly tightened, put a turn or a half on the tuning screw until the highest readings are set around 40Hz (Cascade Fat Head type body, for other types of bodies you'll need to google around ). Clockwise loosens the tension and moves the tuning lower, counterclockwise tightens the tension and lifts the tuning resonance.
Only 0.8µ ribbon, less than 1/1000mm!
Encouraged by the success, especially in the tuning phase which made the process so controllable, I finally decided to try a ribbon of only 0.8µ thin! This last step from 1.2 µ saves another 30% of ribbon mass. The ribbon mass is less than 1/3 of the mass of a 2.5µ ribbon and less than a half of a 1.8µ ribbon.
All said above about the 1.2 foil hold with the 0.8 - again slightly more easily damaged, slightly more difficult to install, but as easy to tune. But the ribbon sure is thin, it tends to fly all over the place with moving air when not attached. You can't breath while installing. When done, even moving around in the studio with the microphone in hand may be hazardous. To be safe, it is best to cover the mic head when taken out of the box and carried to the mic stand. This is no news to Coles 4038 owners.
Comparing 2.5 vs 0.8 ribbons
Here is a short sample video from Logic Pro X, recorded with a simple setup of two microphones, one with 2.5µ (Cascade Fat Head compatible), the other with 0.8µ ribbon. Both mics have the Lundahl LL2912 transformer. They are positioned horizontally side by side 75cm above the snare. No other tracks is involved or mics used. The channels have been calibrated to equal gain levels.
The setup is obviously not ideal to record a complete drumset, but the focus is at the differences of the mics. Both channels have a multimeter attached, nailing the highest readings across the frequency field. Also a channel EQ meter is attached in analysing mode, displaying a continuous live frequency span of the corresponding channels. As seen, all parameters are set to zero level, so no EQing takes place. No effects is attached neither to the recorded channels or the output channel, nor is there any subsequent manipulation of the recording.
Stop the video here and there or use the slider to move around the sample. This freezes the multimeter readings and the frequency response display and allows time to compare the differences.
Summing up - is it worth the trouble?
I don't have the equipment to measure a charasteristics curve of the mic in my humble home studio. But both by other measurable charasteristics and by ear the transition between the stock microphone and last modification is incredible. The microphones output is increased by even as much as 8-9dB, the effective high frequency response is extended by 3000-4000 Hz, and the clarity of sound, sensitivity and transient response is impressive. As seen and heard, even after transformer upgrade, the difference between the decent 2.5µ and the ultimate 0.8µ ribbon is remarkable, as much as 5dB in gain..
The thinnest 0.8µ ribbon is probably impractically fragile for a variety of situations. It's great in the studio, though, if not because of the frequency response, but because of the sensitivity and and output gain. If the sounds tend to get too trenchant or there is ovehelming cymbal washing, you can always EQ the high end without compromising the quality. The advantage of different thickness steps depend on the instrument and recording circumstances, but the tuning mechanism is really great, whatever the ribbon thickness. Sonically and technically there is fundamental improvement of recordings by the cost of parts that roughly only doubles or triples the initially low microphone price. Speaking of money, the result is well worth the minor investments. The trouble is all fun if you are you interested to potter around on your own. For myself, this was an exiting experiment, leading me to listen even more carefully to the sound of my drums and recordings. As a final polish, I replaced the dull chromium plating with brass plating giving the mics a classy vintage look - another interesting task.